1. Technical Field of the Invention
This invention relates to a digital ratemeter for counting pulse signals involving radiation events generated at random and measuring input count rate at a predetermined accuracy.
2. Description of the Prior Art
A conventional ratemeter is illustrated in FIG. 1, in which reference numerals 1 and 2 designate a counter and a timer providing starting or stopping signal to the counter 1, respectively.
Another ratemeter of the same type is shown in FIG. 2, in which a reference numeral 1A designates a group of counters consisting of five connected in cascade counters: the first, second, third, fourth and fifth digit counters to which reference numerals 11, 12, 13, 14 and 15 are allocated, respectively. Further reference numerals indicate as follows: 2A a pulse generator which generates reference time pulse, 3A a group of subtraction inputting elements; 31 a first digit subtraction input element which receives an output a of the third digit counter and an output signal from the pulse generator 2A, and delivers the subtraction output to the first counter; 32 a second digit subtraction inputting element which receives an output b of the fourth counter and an output signal from the pulse generator 2A and delivers the subtraction output signal to the second counter; and 33 a third digit subtraction element which receives an output c of the fifth counter and an output signal from the pulse generator 2A and delivering the subtraction output to the third counter.
The mode of operation will be described below. The counter 1 counts pulses incoming at random during a fixed time. The condition under which the counter 1 starts counting is fulfilled by the delivery of pulse signals output from the timer 2 by repeated oscillation of it to the reset input of the counter 1. The interval of pulse generation by the timer 2 is preset to T seconds. The counting pattern of the counter 1 is illustrated in FIG. 1(B) as the dependence of count value on time lapse. Thus, an average value N (cps) of the count rates in FIG. 1(A) is obtained in the process reading out count value (n) by an external device (not shown) directly before every resetting, and then applying to the count value a predetermined arithmetical operation by the use of a counting time period T seconds. For example in FIG. 1(B), count value n(t.sub.1) is found at time t.sub.1 and count value n(t.sub.2) at time t.sub.2, and the rates at both times are expressed, respectively, as EQU N(t.sub.1)=n(t.sub.1)/T, N(t.sub.2)=n(t.sub.2)/T (1)
The above-mentioned ratemeter executes repeatedly continual counting and outputs count rates intermittently.
The operational mode of another prior art ratemeter is diagrammed in FIG. 2.
The group of counters 1A serves for counting input pulse signals incoming at random. The counter is a decimal 5 digits counter composed of five connected in cascade decimal counters, each being constructed with a N-bit binary counter giving 2.sup.N representation as a basic element. The first digit counter 11 shown counts (pulses output from) an input pulse generator 2A, and subtracts the count value of the third digit counter 13 at a fixed time intervals synchronously with output pulses of the pulse generator 2A. Also the above-mentioned first digit counter 11 outputs count value N.sub.1(t) changing (increasing or decreasing) every moment as decimal first-digit count value N.sub.1(t), and delivers a carry signal to the input of the next higher or second digit counter when the count value N.sub.1(T) amounts to 10. The second and third digit counters 12, 13 operate in the same way as the first digit counter 11. The fourth- or fifth-digit counter 14 or 15 does not receive subtraction counts from the higher digit counter but performs only counting of overflow signals from the lower digit counter. In this way, count values N.sub. 1(t), N.sub.2(t), N.sub.3(t), N.sub.4(t) and N.sub.5(t) are observed at time t on the concerned counters. The output count rate N.sub.(t) is expressed as EQU N.sub.(t) ={N.sub.1(t) +10.sup.1 .times.N.sub.2(t) +10.sup.2 .times.N.sub.3(t) +10.sup.3 .times.N.sub.4(t) +10.sup.4 .times.N.sub.5(t) }/Te (2)
wherein Te is average equivalent integral time in seconds.
In the example diagrammed in FIG. 2, count rate is represented by a decimal t-digits and 1/100 of count value is subtracted every T seconds, hence output count rate per equivalent integral time Te is continuously read-out. Of the prior art digital ratemeters designed, the one illustrated in FIG. 1 has disadvantages of continuous and iterative counting operation and the resulting intermittent rate output. The other illustrated in FIG. 2 accomplishes continuous counting and rate output, but has drawback of wide-range input count rate and inevitable complication of system to attain necessary accuracy.